Elastomer foams have excellent cushioning properties and are advantageously used for sealing materials, cushioning materials, pat materials, and the like. For example, polyester elastomer foams are used as a dustproofing material, a cushioning material, or the like for liquid crystal displays, plasma displays, organic EL displays, and the like of electric or electronic appliances such as cellular phones and digital cameras.
Under such a situation, an uncrosslinked type or crosslinked type polyolefin elastomer foam has been known as an elastomer foam (refer to Patent Literature 1). However, since polyolefin elastomers have a large permanent set, it may be difficult to maintain the thickness and shape required as a sealing material at the time of punching (particularly, at the time of narrow width processing), resulting in the problem of reducing processability and product characteristics. Further, the problem of the permanent set becomes more remarkable under high temperature conditions. Solution of the problem of the permanent set is a challenge to conventional polyolefin elastomer foams. In addition, there is a demand for providing a foam having better heat resistance.
For example, a thermoplastic polyester resin foam suitable for reduction in size, weight, and thickness for electric or electronic appliances has been known (refer to Patent Literature 2). This thermoplastic polyester resin foam has a small compression residual strain and is excellent in processability. However, in the electric or electronic appliance field, there is a demand for providing a thermoplastic polyester resin foam which has a micro cell structure and is further excellent in compression set characteristics, particularly excellent in compression set characteristics at high temperatures. Furthermore, when this thermoplastic polyester resin foam is blackened by adding a colorant, the resulting foam may have deteriorated permanent set characteristics or may not be able to form a micro cell structure.